Let's say 6,7,8 are all taken, and l tried to insert data with id = 6. The purpose of the trigger is to find the next available number. However, MySQL does not recognize new.id
Or, can l alter auto_increment's value?
Why am l doing this? Because in OracleDB, the sequence generator will increment(and eventually find that available number) whereas MySQL's sequence generator won't increment if a duplicate primary key is generated somehow.
tried to replace "new.id = #valid" with "alter table wooster_brush_employee auto_increment = #valid" in trigger, but it did not work.
create table wooster_brush_employee(
id int primary key auto_increment,
first_name varchar(15),
last_name varchar(20),
username varchar(10),
password varchar(15),
email varchar(30)
);
delimiter //
create trigger validate_id before insert on wooster_brush_employee
for each row
set #old = last_insert_id();
set #valid = last_insert_id();
call wooster_brush_employee_id_validator(#old, #valid);
set NEW.id = #valid;
end;
delimiter;
I believe that your whole approach here is off kilter, and you don't even need to use this trigger. The point of an auto increment column, in either MySQL or Oracle, is that the database handles the problem of finding the next available number in the sequence. While the auto increment contract does not guarantee that the next value found will be greater than every value already in the column, it does guarantee that the next value will be unique.
So, if you want to make use of MySQL's auto increment functionality, then next time you insert, simply omit id from the column list:
INSERT INTO wooster_brush_employee (first_name, last_name, username, password, email)
VALUES
('Jon', 'Skeet', 'jonskeet', '*****", 'jon.skeet#google.com');
Since id was omitted, MySQL will automatically generate the next value in the sequence behind the scenes.
Related
I need to create an entity form which has unique identification column in the database and its not a primary key column and I need to display that in the form creation page. I've set this column as UNIQUE and not null. Now whenever I create a new user, employee or any entity I need to generate a sequence number like in this format and display it in the form,
ID_001, ID_002 ... ID_00N and so on.
EMP_001, EMP_002 ... EMP_00N and so on.
and when the three digit sequence number reaches the max limit of 999. The seqence number should generate the number as four digits until 9999 is reached and the employee code will be like EMP_1000. So when I get the last insert id when creating the form, it will not work if more than one user is creating simultaneously and there would be a conflict. I thought about creating a new table like sequence_generator. Where I store key-value pair of the the entity-last insert id. So whenver next insert happens I can read from this table and increment by 1 for new sequence numbers.
So How do I best implement this sequence generating which is also Unique in Java/MySql/Mybatis/Spring?
I would create my own sequencing implementation using triggers. I am not very familiar with mysql. So, take my examples as a pseudo-code. Your trigger would look like:
Create a table with no auto-increment. Example:
CREATE TABLE EMPLOYEE (
ID CHAR(30), NAME CHAR(30)
)
Create a trigger with the logic to auto-increment your columns. Similar to:
CREATE TRIGGER EMPLOYEE_SEQUENCE BEFORE INSERT ON EMPLOYEE
FOR EACH ROW
BEGIN
SET #PREPENDED_ZEROS = '';
SET #ID_AS_NUMBER = CAST(SUBSTRING(ID,3) AS INT) + 1;
IF #ID_AS_NUMBER < 10 THEN
SET #PREPENDED_ZEROS = '00';
ELSEIF #ID_AS_NUMBER < 100 THEN
SET #PREPENDED_ZEROS = '0';
END IF;
SET NEW.ID = 'EMP_' || #PREPENDED_ZEROS || #ID_AS_NUMBER;
END;
I have a table with 3 fields: Id(PK,AI), Name(varchar(36)), LName(varchar(36)).
I have to insert name and last name, Id inserts automatically because of it's constraints,
Is There a way to Jump id auto increment value when it reaches 6?
for instance do this 7 times:
Insert Into table(Name, LName) Values ('name1', 'lname1') "And jump id to 7 if it is going to be 6"
It may sound stupid to do this but I have the doubt.
Also Jump and do not record id 6.
record only, 1-5, 7,8,9 and so on
What I want to achieve starts from a Union:
Select * From TableNames
Union All
Select * From TableNames_general
In the TableNames_general I assign it's first value so that when the user sees the table for the first time it will be displayed the record I inserted.
The problem comes when the user inserts a new record, if the Id of the inserted record is the same as the one I have inserted it will be duplicated, that is why I want to achieve when the users inserts one record and if the last insert id already exists just jump that record. this is because I must have different ids due to its relationship among child tables.
Identity column generate values for you, And its best left this way, You have the ability to insert specific values in Identity column but its best left alone and let it generate values for you.
Imagine you have inserted a value explicitly in an identity column and then later on Identity column generates the same value for you, you will end up with duplicates.
If you want to have your input in that column then why bother with identity column anyway ??
Well this is not the best practice but you can jump to a specific number by doing as follows:
MS SQL SERVER 2005 and Later
-- Create test table
CREATE TABLE ID_TEST(ID INT IDENTITY(1,1), VALUE INT)
GO
-- Insert values
INSERT INTO ID_TEST (VALUE) VALUES
(1),(2),(3)
GO
-- Set idnentity insert on to insert values explicitly in identity column
SET IDENTITY_INSERT ID_TEST ON;
INSERT INTO ID_TEST (ID, VALUE) VALUES
(6, 6),(8,8),(9,9)
GO
-- Set identity insert off
SET IDENTITY_INSERT ID_TEST OFF;
GO
-- 1st reseed the value of identity column to any smallest value in your table
-- below I reseeded it to 0
DBCC CHECKIDENT ('ID_TEST', RESEED, 0);
-- execute the same commad without any seed value it will reset it to the
-- next highest idnetity value
DBCC CHECKIDENT ('ID_TEST', RESEED);
GO
-- final insert
INSERT INTO ID_TEST (VALUE) VALUES
(10)
GO
-- now select data from table and see the gap
SELECT * FROM ID_TEST
If you query the database to get the last inserted ID, then you can check if you need to increment it, by using a parameter in the query to set the correct ID.
If you use MSSQL, you can do the following:
Before you insert check for the current ID, if it's 5, then do the following:
Set IDENTITY_INSERT to ON
Insert your data with ID = 7
Set IDENTITY_INSERT to OFF
Also you might get away with the following scenario:
check for current ID
if it's 5, run DBCC CHECKIDENT (Table, reseed, 6), it will reseed the table and in this case your next identity will be 7
If you're checking for current identity just after INSERT, you can use SELECT ##IDENTITY or SELECT SCOPE_IDENTITY() for better results (as rcdmk pointed out in comments)
Otherwise you can just use select: SELECT MAX(Id) FROM Table
There's no direct way to influence the AUTO_INCREMENT to "skip" a particular value, or values on a particular condition.
I think you'd have to handle this in an AFTER INSERT trigger. An AFTER INSERT trigger can't update the values of the row that was just inserted, and I don't think it can make any modifications to the table affected by the statement that fired the trigger.
A BEFORE INSERT trigger won't work either, because the value assigned to an AUTO_INCREMENT column is not available in a BEFORE INSERT trigger.
I don't believe there's a way to get SQL Server IDENTITY to "skip" a particular value either.
UPDATE
If you need "unique" id values between two tables, there's a rather ugly workaround with MySQL: roll your own auto_increment behavior using triggers and a separate table. Rather than defining your tables with AUTO_INCREMENT attribute, use a BEFORE INSERT trigger to obtain a value.
If an id value is supplied, and it's larger than the current maximum value from the auto_increment column in the dummy auto_increment_seq table, we'd need to either update that row, or insert a new one.
As a rough outline:
CREATE TABLE auto_increment_seq
(id INT NOT NULL PRIMARY KEY AUTO_INCREMENT) ENGINE=MyISAM;
DELIMITER $$
CREATE TRIGGER TableNames_bi
BEFORE INSERT ON TableNames
FOR EACH ROW
BEGIN
DECLARE li_new_id INT UNSIGNED;
IF ( NEW.id = 0 OR NEW.id IS NULL ) THEN
INSERT INTO auto_increment_seq (id) VALUES (NULL);
SELECT LAST_INSERT_ID() INTO li_new_id;
SET NEW.id = li_new_id;
ELSE
SELECT MAX(id) INTO li_max_seq FROM auto_increment_seq;
IF ( NEW.id > li_max_seq ) THEN
INSERT INTO auto_increment_seq (id) VALUES (NEW.id);
END IF;
END IF;
END$$
CREATE TRIGGER TableNames_ai
AFTER INSERT ON TableNames
FOR EACH ROW BEGIN
DECLARE li_max_seq INT UNSIGNED;
SELECT MAX(id) INTO li_max_seq FROM auto_increment_seq;
IF ( NEW.id > li_max_seq ) THEN
INSERT INTO auto_increment_seq (id) VALUES (NEW.id);
END IF;
END;
DELIMITER ;
The id column in the table could be defined something like this:
TableNames
( id INT UNSIGNED NOT NULL DEFAULT 0 PRIMARY KEY
COMMENT 'populated from auto_increment_seq.id'
, ...
You could create an identical trigger for the other table as well, so the two tables are effectively sharing the same auto_increment sequence. (With less efficiency and concurrency than an Oracle SEQUENCE object would provide.)
IMPORTANT NOTES
This doesn't really insure that the id values between the tables are actually kept unique. That would really require a query of the other table to see if the id value exists or not; and if running with InnoDB engine, in the context of some transaction isolation levels, we might be querying a stale (as in, consistent from the point in time at the start of the transaction) version of the other table.
And absent some additional (concurrency killing) locking, the approach outline above is subject to a small window of opportunity for a "race" condition with concurrent inserts... the SELECT MAX() from the dummy seq table, followed by the INSERT, allows a small window for another transaction to also run a SELECT MAX(), and return the same value. The best we can hope for (I think) is for an error to be thrown due to a duplicate key exception.
This approach requires the dummy "seq" table to use the MyISAM engine, so we can get an Oracle-like AUTONOMOUS TRANSACTION behavior; if inserts to the real tables are performed in the context of a REPEATABLE READ or SERIALIZABLE transaction isolation level, reads of the MAX(id) from the seq table would be consistent from the snapshot at the beginning of the transaction, we wouldn't get the newly inserted (or updated) values.
We'd also really need to consider the edge case of an UPDATE of row changing the id value; to handle that case, we'd need BEFORE/AFTER UPDATE triggers as well.
how can i create a trigger function before adding/updating,the function should check records that have the same id (i.e comparison by id with existing objects that have the same property as the temporary_object)If a record with the id is found, then that entry is set to the time_dead, and then it adds an entry containing the corresponding values of the attributes found in that record (except those that are set for a new record), when time_dead is empty then time_create of a new time is equal to that time at the current moment . Thus,a new record time_create is like the time_dead's ancestor.
If a record with that id is found then it is added to the database with the establishment as the time_create of the current time.
for example here is a simple explanation(just for explanation purposes)
id time_create time-dead student amount
1 06.12 07.12 henry 500
1 07.12 henry 1000
so if a student called henry with id 1 entered a room at 06.12 and left at 07.12 the next time he enters another room again time_dead will be equal to time_create(so time_dead of old entry and time_create of new entry - will be equal)
these are my tables below in sql format
CREATE TABLE temporary_object
(
id integer NOT NULL,
time_create timestamp without time zone NOT NULL,
time_dead timestamp without time zone,
CONSTRAINT temporary_object_pkey PRIMARY KEY (id, time_create)
)
CREATE TABLE persons
(
fname text,
fsurname text,
)
INHERITS (temporary_object)
CREATE TABLE rooms
(
roomnum integer,
course integer,
passport text,
students_number text
)
INHERITS (temporary_object)
this is what i am trying to do but im afraid i do not know how to finish it but im 100% not right may some help out
CREATE TRIGGER trigger2
BEFORE INSERT OR UPDATE
ON persons
FOR EACH ROW
EXECUTE PROCEDURE func1();
and this is the function
CREATE OR REPLACE FUNCTION func1() RETURNS TRIGGER AS $persons$
DECLARE
time_create integer;
time_dead timestamp;
id timestamp;
BEGIN
IF (TG_OP = 'INSERT') THEN
time_create=
I can't tell you what I'm missing from your question, but I try to answer what I think I understood.
Row level triggers can access the version of the row affected with the NEW and OLD variables (depending on TG_OP). In this case, you can use NEW:
CREATE OR REPLACE FUNCTION func1()
RETURNS TRIGGER AS
$persons$
DECLARE
i integer;
BEGIN
IF TG_OP = 'INSERT'
THEN
UPDATE persons
SET time_dead = NEW.time_create
WHERE
id = NEW.id -- we are looking for the same ID
AND time_dead IS NULL
;
ELSE -- UPDATE
-- do here something
END IF;
END;
$persons$
LANGUAGE plpgsql;
This is only a starter, modify it to your needs.
To be more clear:
The table thetable (id int, username varchar(30), password varchar(30), last_successful_login timestamp, last_unsuccessful_login timestamp, another_variable varchar(30)) has the following row: (1, "tgh", "pass", 0, 0, "another")
1) Wrong User/Pass Pair, but there is a row with the username
I want select id from thetable where username="tgh" and password="wrongpass" and another_variable="another"; to update the last_unsuccessful_login columns of all the rows with username="tgh" AND another_variable="another" (which is unique, there can't be two rows with ("tgh", "another") pair. There can be ("tgh", "another2") though.) to CURRENT_TIMESTAMP.
So the example row would be (1, "tgh", "pass", 0, CURRENT_TIMESTAMP, "another"), after the "select" query that does not completely match.
To be even more clear, I am trying to avoid running an extra update with only username="tgh" and another_variable="another" on the table, i.e. update thetable set last_unsuccessful_login=CURRENT_TIMESTAMP where username="tgh" and another_variable="another";, according to the result of the select.
2) Correct User/Pass Pair
Also, if all three username and password and another_variable matches, this time I want to set the last_successful_login to CURRENT_TIMESTAMP.
That would make the example row `(1, "tgh", "pass", CURRENT_TIMESTAMP, 0, "another")
What is the most efficient way to do this?
The short answer to your question is no, it is not possible for a SELECT statement to cause or trigger an update. (The caveat here is that a SELECT statement can call a FUNCTION (MySQL stored program) which can perform an UPDATE.)
You can't get around issuing an UPDATE statement; an UPDATE statement has to be issued from somewhere, and a SELECT statement cannot "trigger" it.
It is possible to have a single UPDATE statement do the check of the supplied password against the current value in the password column, and set both the last_successful_login and last_unsuccessful_login columns, e.g.:
UPDATE thetable
SET last_successful_login =
IF(IFNULL(password,'')='wrongpass',CURRENT_TIMESTAMP,0)
, last_unsuccessful_login =
IF(IFNULL(password,'')='wrongpass',0,CURRENT_TIMESTAMP)
WHERE username='tgh'
AND another_variable='another'
So, you could issue an UPDATE statement first; and then issue a SELECT statement.
If you want to minimize the number of "roundtrips" to the database, at the cost of additional complexity (making it harder for someone else to figure out what is going on) you could put the UPDATE statement into a stored program. If you put this into a function, you could set the return value to indicate whether the login was successful.
SELECT udf_login('username','wrongpass','another')
So, from your application, it looks like you are doing a login check, but the called function can perform the UPDATE.
CREATE FUNCTION `udf_login`
( as_username VARCHAR(30)
, as_password VARCHAR(30)
, as_another_variable VARCHAR(30)
) RETURNS INT
READS SQL DATA
BEGIN
UPDATE `thetable`
SET `last_successful_login` =
IF(IFNULL(`password`,'')=IFNULL(as_password,''),CURRENT_TIMESTAMP,0)
, `last_unsuccessful_login` =
IF(IFNULL(`password`,'')=IFNULL(as_password,''),0,CURRENT_TIMESTAMP)
WHERE `username` = as_username
AND `another_variable` = as_another_variable;
-- then perform whatever checks you need to (e.g)
-- SELECT IFNULL(t.password,'')=IFNULL(as_password,'') AS password_match
-- FROM `thetable` t
-- WHERE t.username = as_username
-- AND t.another_variable = as_another_variable
-- and conditionally return a 0 or 1
RETURN 0;
END$$
Say I have a MySQL table with an auto incrementing id field, then I insert 3 rows. Then, I delete the second row. Now the id's of the table go 1,3. Can I get MySQL to correct that and make it 1,2 without having to write a program to do so?
MySQL won't let you change the indexing of an Auto-Index column once it's created. What I do is delete the Auto-Index column and then add a new one with the same name, mysql will index the newly generated column with no gaps. Only do this on tables where the Auto-Index is not relevant to the rest of the data but merely used as a reference for updates and deletes.
For example I recently did just that for a table containing proverbs where the Auto-Index column was only used when I updated or deleted a proverb but I needed the Auto-Index to be sequential as the proverbs are pulled out via a random number between 1 and the count of the proverbs, having gaps in the sequence could have led to the random number pointing to a non-existant index.
HTH
Quoting from The Access Ten Commandments (and it can be extensible to other RDBMS: "Thou shalt not use Autonumber (or Auto Incremental) if the field is meant to have meaning for thy users".
The only alternative I can think of (using only MySQL) is to:
Create a trigger that adds the row number to a column (not the primary key)
Create a procedure to delete rows and update the row number (I couldn't make this work with triggers, sorry)
Example:
create table tbl_dummy(
id int unsigned not null auto_increment primary key,
row_number int unsigned not null default 0,
some_value varchar(100)
);
delimiter $$
-- This trigger will add the correct row number for each record inserted
-- to the table, regardless of the value of the primary key
create trigger add_row_number before insert on tbl_dummy
for each row
begin
declare n int unsigned default 0;
set n = (select count(*) from tbl_dummy);
set NEW.row_number = n+1;
end $$
-- This procedure will update the row numbers for the records stored
-- after the id of the soon-to-be-deleted record, and then deletes it.
create procedure delete_row_from_dummy(row_id int unsigned)
begin
if (select exists (select * from tbl_dummy where id = row_id)) then
update tbl_dummy set row_number = row_number - 1 where id > row_id;
delete from tbl_dummy where id = row_id;
end if;
end $$
delimiter ;
Notice that you'll be forced to delete the records one by one, and you'll be forced to get the correct primary key value of the record you want to delete.
Hope this helps